U.S. patent application number 15/566815 was filed with the patent office on 2018-03-15 for water treatment system and water treatment process.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Kyohei AKETAGAWA, EIJI IMAMURA, Nozomu YASUNAGA.
Application Number | 20180072597 15/566815 |
Document ID | / |
Family ID | 56871723 |
Filed Date | 2018-03-15 |
United States Patent
Application |
20180072597 |
Kind Code |
A1 |
IMAMURA; EIJI ; et
al. |
March 15, 2018 |
WATER TREATMENT SYSTEM AND WATER TREATMENT PROCESS
Abstract
A water treatment system including: a biological treatment stage
for treating an organic wastewater by an action of a microorganism;
an ozone gas producing stage for generating ozone gas; a sludge
transferring stage for withdrawing and transferring a part of the
microorganism-mixed liquid in the biological treatment stage; an
ozone treatment stage for bringing ozone into contact with the part
of the microorganism-mixed liquid transferred; and a treated liquid
returning stage for returning the treated liquid after the ozone
treatment from the ozone treatment stage to the biological
treatment stage. Undecomposed aggregated microorganisms after the
ozone treatment are separated and concentrated, and an ozone
treatment is selectively applied to the aggregated undecomposed
microorganisms thus separated and concentrated.
Inventors: |
IMAMURA; EIJI; (Tokyo,
JP) ; AKETAGAWA; Kyohei; (Tokyo, JP) ;
YASUNAGA; Nozomu; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
56871723 |
Appl. No.: |
15/566815 |
Filed: |
May 18, 2015 |
PCT Filed: |
May 18, 2015 |
PCT NO: |
PCT/JP2015/064138 |
371 Date: |
October 16, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2253/106 20130101;
B01D 53/04 20130101; C02F 3/26 20130101; C02F 11/06 20130101; C02F
2203/006 20130101; C02F 1/78 20130101; C02F 1/44 20130101; C02F
3/1221 20130101; C02F 2101/30 20130101; C02F 2209/40 20130101; C02F
2103/32 20130101; C02F 2103/346 20130101; Y02W 10/10 20150501; C02F
3/1252 20130101; B01D 2257/106 20130101; C02F 3/1268 20130101; B01D
53/66 20130101; C02F 2201/782 20130101 |
International
Class: |
C02F 3/26 20060101
C02F003/26; C02F 3/12 20060101 C02F003/12; C02F 1/44 20060101
C02F001/44; C02F 1/78 20060101 C02F001/78 |
Claims
1: A water treatment system, which includes a microorganism
treatment unit configured to treat a water with a microorganism, a
withdrawing unit configured to withdraw a partial water from the
water treated by the microorganism treatment unit, a water tank
having a height in the vertical direction and configured so that
the partial water withdrawn by the withdrawing unit flows therein
and is stored therein, an ozone generation unit configured to
generate ozone, and an ozone reaction unit configured to allow the
partial water to react with the ozone generated by the ozone
generation unit, and which treats the water, the water treatment
system comprising: a returning unit connected to an underside in
the vertical direction of the water tank, and configured to return
at least a part of the partial water stored in the water tank to
the microorganism treatment unit, and a circulating means
configured to withdraw the partial water stored in the water tank
from a lower portion of the water tank and circulate the partial
water to the ozone reaction unit; and a flow-in means configured to
allow the partial water circulated by the circulation means to
react with the ozone generated by the ozone generation unit and to
flow again into the water tank, wherein the water tank is provided
with a moving means that moves the partial water downwardly flowing
therein upwardly in the vertical direction and a flow regulation
means that is disposed above the moving means and regulates flow of
the partial water moved by the moving means, and the circulation
means circulates the partial water moved by the moving means,
regulated in flow by the flow regulation means, and stored in the
lower portion of the water tank.
2: The water treatment system according to claim 1, wherein the
moving means is a baffle plate, and the partial water reacted by
the ozone reaction unit flows-in from above in the vertical
direction toward the baffle plate.
3: The water treatment system according to claim 2, wherein the
flow regulation means includes a plurality of plate-like members
spaced apart from each other, the horizontal cross sectional area
of the space between the plurality of plate-like members is 10 to
50% relative to the horizontal cross sectional area of the water
tank, and the plurality of plate-like members are each inclined by
0 to 60 degrees with respect to the vertical direction.
4: The water treatment system according to claim 2, wherein the
flow regulation means includes a plurality of cylindrical members,
the horizontal cross sectional area of the hollowed portions of the
plurality of cylindrical members is 10 to 50% relative to the
horizontal cross sectional area of the water tank, and the
plurality of cylindrical members are each inclined by 0 to 60
degrees with respect to the vertical direction.
5: The water treatment system according to claim 1, wherein the
ozone reaction unit includes a venturi device configured to inject
the ozone generated into the partial water circulated by the
circulation means.
6: The water treatment system according to claim 1, which includes
a concentration unit configured to concentrate the ozone generated,
and is configured to allow the ozone concentrated by the
concentration unit to react with the partial water circulated by
the circulation means.
7: A water treatment process which includes a treating step for
treating a water with a microorganism, the water treatment process
comprising: a withdrawing step for withdrawing a partial water from
the water treated; a storing step for allowing the partial water
withdrawn to flow into a water tank having a height in the vertical
direction and storing the partial water therein; a moving step for
moving the partial water flowing downwardly in the vertical
direction in the water tank upwardly in the vertical direction; a
flow regulating step for regulating flow of the partial water
moved; a circulating step for withdrawing at least a part of the
partial water regulated in flow and stored in the water tank from a
lower portion of the water tank and circulating the at least a part
of the partial water to the ozone reaction unit, a generating step
for generating ozone; a reacting step for allowing the partial
water circulated to react in the ozone reaction unit with the ozone
generated; a re-flow-in step for allowing the partial water reacted
to flow again into the water tank, and a retreating step for
treating again a stored substance moved upwardly, regulated in
flow, and stored in the lower portion of the water tank, after the
re-flow-in, with the microorganism.
8: The water treatment process according to claim 7, wherein the
time period from starting the withdrawing step to starting again
the withdrawing step is 30% or more of the time period for treating
the water with the microorganism.
9: The water treatment process according to claim 8, wherein the
generating step includes a concentrating step for concentrating the
ozone generated, and the reacting step allows the partial water
circulated to react with the ozone concentrated.
10: The water treatment process according to claim 7, wherein the
treating step and the retreating step perform a treatment by using
a membrane bioreactor process.
Description
TECHNICAL FIELD
[0001] The present invention relates to a water treatment system
for treating a water containing organic substances, and a water
treatment process.
BACKGROUND ART
[0002] Water treatment systems using a process for treating a
wastewater or other waters with microorganisms, such as a
conventional activated sludge process, have heretofore known. Such
a water treatment system uses a microorganism that can consume
organic substances as substrates, and a treatment for purifying a
water is carried out by allowing the microorganism to consume
organic substances in the water as substrates.
[0003] When microorganisms consume organic substances in a water
through the water treatment, the microorganisms in the water will
grow. For example, in a conventional activated sludge process, a
sedimentation tank is placed as a subsequent stage of an aeration
tank so as to store microorganisms flowing out from the aeration
tank. However, when the microorganisms excessively grow,
microorganisms flowing out of the aeration tank may exceed the
storage allowance of the sedimentation tank, and therefore the
excessively grown microorganisms have to be discharged out of the
water treatment system as excess sludge. In addition, when the
amount of microorganisms in the aeration tank excessively increases
in the membrane bioreactor process (MBR), clogging of a membrane
may be caused, and therefore the excessively grown microorganisms
have to be appropriately discharged as excess sludge so that the
amount of the microorganisms falls within a proper range.
[0004] As a method for disposal of the excess sludge discharged, a
method using incineration, a method of disposal by fermenting the
sludge under an anaerobic condition (digestion treatment), and the
like may be employed. Any method requires a great deal of energy
and cost. Accordingly, in a water treatment process using
microorganisms, reduction in the amount of excess sludge discharged
is demanded.
[0005] PTL 1 proposes a water treatment system using ozone for
reducing the amount of excess sludge discharged. In this water
treatment system, a water containing microorganisms grown through a
treatment is brought into contact with ozone to decompose the
microorganisms, and a water treatment by the microorganisms is
applied again using organic substances contained in the water and
the microorganisms decomposed by the ozone (referred to as
decomposed microorganisms) as substrates, thereby reducing the
amount of excess sludge discharged.
CITATION LIST
Patent Literature
[0006] PTL 1: JP-A-11-42494
SUMMARY OF INVENTION
Technical Problem
[0007] In the water treatment disclosed in PTL 1, a
microorganism-mixed liquid which is a treated water to be subjected
to the water treatment exists in an aeration tank containing
microorganisms, and the microorganism-mixed liquid which may
contain the microorganisms grown through the water treatment is
withdrawn from the aeration tank and ozone is injected into a part
of the withdrawn microorganism-mixed liquid via an ejector, and the
microorganism-mixed liquid resulting from the ozone treatment by
injecting ozone is returned to the aeration tank, thereby achieving
the reduction of the amount of excess sludge discharged.
[0008] However, the above method using ozone still has room for
improvement. For example, in this method, the microorganisms are
decomposed by being brought into a contact reaction with ozone, and
ozone is consumed by not only a reaction with the undecomposed
microorganisms, but also reactions with the remaining organic
substances, the decomposed microorganisms which have already been
decomposed, and an organic substance leaking from the decomposed
microorganisms. The reactions of ozone with the remaining organic
substances, the decomposed microorganisms, and the organic
substance leaking from the decomposed microorganisms, which are not
targets of the reaction, lead to a reduced efficiency of ozone
reaction with the grown microorganisms which are the target of the
reaction. For this reason, for achieving a sufficient effect of
excess sludge reduction, it is required to take into consideration
the amount of ozone consumed by reactions with substances that are
not targets of the reaction.
[0009] The present invention is made for solving the above problem,
and has an object to provide a water treatment system and a
wastewater treatment process in which grown undecomposed
microorganisms are allowed to selectively react with ozone to
maintain the reaction efficiency between the microorganisms as the
target of the reaction and ozone at a high level, and a high effect
of excess sludge reduction can be achieved with a small amount of
ozone injected.
Solution to Problem
[0010] The water treatment system according to the present
invention includes a microorganism treatment unit configured to
treat a water with microorganisms, a withdrawing unit configured to
withdraw a partial water from the water treated by the
microorganism treatment unit, an ozone generation unit configured
to generate ozone, and an ozone reaction unit configured to allow
the partial water withdrawn by the withdrawing unit to react with
ozone generated by the ozone generation unit. The water treatment
system according to the present invention also includes a water
tank having a height in the vertical direction and configured so
that the partial water reacted by the ozone reaction unit flows
therein and is stored therein, and a returning unit connected to an
underside in the vertical direction of the water tank and
configured to return at least a part of the partial water stored in
the water tank to the microorganism treatment unit. The water tank
includes a moving means that moves the partial water flowing
therein upwardly in the vertical direction and a flow regulation
means that is disposed above the moving means and regulates flow of
the partial water moved by the moving means.
[0011] The water treatment process according to the present
invention includes a treating step for treating a water with
microorganisms. The water treatment process according to the
present invention also includes a withdrawing step for withdrawing
a partial water from the water treated, and a generating step for
generating ozone, a reacting step for allowing the partial water
withdrawn to react with the ozone generated, a storing step for
allowing the partial water reacted to flow into a water tank having
a height in the vertical direction to store the partial water
therein, a moving step for moving the partial water flowing therein
upwardly in the vertical direction, a flow regulating step for
regulating flow of the partial water moved, and a retreating step
for treating again at least a part of the partial water regulated
in flow with microorganisms.
Advantageous Effects of Invention
[0012] According to the present invention, undecomposed
microorganisms which are a reaction target can be allowed to
selectively react with ozone. Accordingly, it is possible to
maintain the reaction efficiency between the undecomposed
microorganisms and ozone at a high level, achieving a high effect
for excess sludge reduction with a relatively small amount of ozone
injected. In addition, since the water treatment can be performed
with a relatively small amount of ozone injected, it is possible to
suppress toxicity of ozone which may occur due to a high
concentration of ozone, thereby achieving a good and stable water
quality after treatment.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a schematic diagram showing a configuration of a
water treatment system according to Embodiment 1.
[0014] FIG. 2 is a schematic view showing an example of a guide
pipe included in a water treatment system.
[0015] FIG. 3 is a schematic view showing an example of a guide
pipe included in a water treatment system.
[0016] FIG. 4 is a three dimensional view for explaining an example
of a flow regulator included in a water treatment system.
[0017] FIG. 5 is a three dimensional view for explaining an example
of a flow regulator included in a water treatment system.
[0018] FIG. 6 is a cross sectional view for explaining an example
of a structure of a flow regulator.
[0019] FIG. 7 is a cross sectional view for explaining an example
of a structure of a flow regulator.
[0020] FIG. 8 is a cross sectional view for explaining a structure
of a sludge concentration and separation device and a flow of water
in a tank.
[0021] FIG. 9 is a schematic view for explaining an aperture ratio
of a flow regulator.
[0022] FIG. 10 is a schematic view for explaining an inclination
angle of a flow regulator.
[0023] FIG. 11 is a schematic diagram showing a configuration of a
water treatment system according to Embodiment 2.
[0024] FIG. 12 is a schematic diagram showing a configuration of a
water treatment system according to Embodiment 3.
[0025] FIG. 13 is a schematic diagram showing a modification
example of the water treatment system according to Embodiment
3.
[0026] FIG. 14 is a schematic diagram showing a configuration of a
water treatment system according to Embodiment 4.
[0027] FIG. 15 is a schematic diagram showing a modification
example of the water treatment system according to Embodiment
4.
[0028] FIG. 16 is a schematic diagram showing a modification
example of the water treatment system according to Embodiment
4.
[0029] FIG. 17 is a schematic diagram showing a configuration of a
water treatment system according to Embodiment 5.
[0030] FIG. 18 is a schematic diagram for explaining a
configuration of an ozone water production unit provided in a water
treatment system.
[0031] FIG. 19 is a schematic diagram for showing a modification
example of the ozone water production unit provided in a water
treatment system.
[0032] FIG. 20 is a graph showing a relation between aperture ratio
and amount of ozone.
[0033] FIG. 21 is a graph showing a relation between number of days
for treatment and BOD removal ratio.
DESCRIPTION OF EMBODIMENTS
[0034] Embodiments of the water treatment system and the water
treatment process disclosed in the present application are
described in detail below with reference to the accompanying
drawings. Incidentally, each of the following Embodiments is merely
an example, and is not to limit the present invention. Embodiment
1.
[0035] FIG. 1 is a schematic diagram showing an example of a water
treatment system according to Embodiment 1. In the water treatment
system, a conventional activated sludge process is applied in a
biological treatment stage.
[0036] The water treatment system includes a component, such as an
aeration tank 1, as an example of a microorganism treatment unit
configured to treat a water with microorganisms. The aeration tank
1 contains an aerobic microorganism capable of utilizing organic
substances as substrates. A wastewater introducing path 3 that
receives a wastewater 2 and a flow-out path 4 that receives a
flow-out water from the aeration tank 1 are connected to the
aeration tank 1. The flow-out path 4 is also connected to a
sedimentation tank 5 and transfers the flow-out water from the
aeration tank 1 to the sedimentation tank 5. A treated water
releasing path 6 is connected to the sedimentation tank 5, and a
supernatant water in the sedimentation tank flows out via the
treated water releasing path 6.
[0037] The wastewater 2, as used herein, is an example of a water
which is a target to be treated in a water treatment system. When
the wastewater 2 is, for example, a municipal sewage, a wastewater
discharged from a food processing plant, a wastewater discharged
from a semiconductor manufacturing plant, and the like, a
relatively large amount of organic substances to be treated are
contained.
[0038] In a water treatment, microorganisms consume the organic
substances in the aeration tank 1, and when the microorganisms
excessively grow, the excessively grown microorganisms become
excess sludge, and the microorganisms flowing out of the aeration
tank 1 may exceed the storage allowance of the sedimentation tank
5.
[0039] In the aeration tank 1, a water-microorganism mixed liquid 7
which is the wastewater 2 in a state where the excessively grown
microorganisms may be contained is stored. Also in the aeration
tank 1, air is released from an air diffuser 9 through an air
introducing path 8 and fed to the microorganism-mixed liquid 7. A
sludge withdrawing pipe 10 is connected to the bottom of the
sedimentation tank 5, and the sludge withdrawing pipe 10 is
connected to a sludge withdrawing pump 11. The ejection side of the
sludge withdrawing pump 11 is divided into a sludge returning pipe
12 and a sludge discharging pipe 13.
[0040] As used herein, a merely "sludge" refers to a collection of
microorganisms, and a "separated sludge" refers to a sludge that is
separated out when microorganisms that have flown out of an
aeration tank are subjected to solid-liquid separation. An "excess
sludge" refers to a sludge that has to be discarded since
microorganisms grow in a biological treatment stage to produce
microorganisms and excess microorganisms are accumulated in the
wastewater treatment system.
[0041] The water treatment system includes an ozone reaction tank
14, and to the ozone reaction tank 14, a sludge transferring pipe
15, a sludge extracting pipe 16, and a waste-ozone releasing path
17 are connected. The sludge transferring pipe 15 is inserted into
the aeration tank 1, and a sludge transferring pump 18 is placed on
the sludge transferring pipe 15. Thus, by the sludge transferring
pump 18, the microorganism-mixed liquid 7 in the aeration tank 1
can be transferred through the sludge transferring pipe 15 into the
ozone reaction tank 14. A sludge circulating pump 19 is connected
to the sludge extracting pipe 16. The ejection side of the sludge
circulating pump 19 is divided into a sludge circulating pipe 20
and a treated liquid returning pipe 21. The sludge circulating pipe
20 is connected to the sludge transferring pipe 15, and the sludge
transferring pipe 15 is connected to a sludge introducing pipe 22
placed in the ozone reaction tank 14. A flowmeter 67 for measuring
a flow rate of a liquid flowing through the pipe and an ejector 23
are provided on the sludge circulating pipe 20.
[0042] The water treatment system also includes an ozone production
device 24, an ozone transferring path 25, and an ozone injecting
path 26. In FIG. 11, the ozone production device 24 includes an
ozone generator 27 and an ozone concentrator 28, and the ozone
transferring path 25 is connected to the ozone generator 27 and the
ozone concentrator 28. The ozone injecting path 26 is connected to
the ozone concentrator 28 and the ejector 23. A flowmeter 66 for
measuring an ozone gas flow rate is provided on the ozone injecting
path.
[0043] The water treatment system further includes a sludge
concentration and separation device 29 in the ozone reaction tank
14, and valves 46 to 52 on the respective pipes. The sludge
concentration and separation device 29 is composed of a baffle
plate 30, a guide pipe 31, and a flow regulator 32.
[0044] The operation of the water treatment system of FIG. 1 having
the above configuration is as follows.
<Biological Treatment Stage>
[0045] The wastewater 2 containing organic substances is introduced
into the aeration tank 1 through the wastewater introducing path
3.
[0046] In the aeration tank 1, the microorganism-mixed liquid 7
containing an aerobic microorganism that can utilize the organic
substances as substrates is stored. Accordingly, in the aeration
tank 1, the organic substances contained in the wastewater 2 are
removed from the water, whereby the wastewater 2 is purified.
[0047] The wastewater 2 purified in the aeration tank 1 is retained
for a prescribed retention time and then flows out through the
flow-out path 4 into the sedimentation tank 1 as a flow-out
water.
[0048] In the sedimentation tank 5, the microorganisms in the
microorganism-mixed liquid 7 flowing therein together with the
flow-out water from the aeration tank are settled and separated
out.
[0049] The separated microorganisms accumulate on the bottom of the
sedimentation tank 5 as a separated sludge 33, while a clear
supernatant water is released from the top of the sedimentation
tank 5 through the treated water releasing path 6.
[0050] The separated sludge 33 accumulating on the bottom of the
sedimentation tank 5 is withdrawn through the sludge withdrawing
pipe 10 by the sludge withdrawing pump 11. The withdrawn separated
sludge 33 is returned through the sludge returning pipe 12 into the
aeration tank 1.
[0051] As described above, since the wastewater treatment has
microorganisms utilize organic substances in a wastewater, the
organic substances can be removed from the wastewater, whereas the
microorganisms grown by utilizing organic substances gradually
accumulate in the system. Accordingly, when solid matter such as
the microorganisms excessively accumulates in the system, the solid
matter is discharged out of the system as an excess sludge through
the sludge discharging pipe 13, and processed as a waste. As
already described, the disposal of the excess sludge requires
enormous energy and cost, and it is required to reduce the amount
of the excess sludge discharged.
<Ozone Gas Producing Stage>
[0052] In Embodiment 1, the ozone gas producing stage includes an
ozone generating stage and an ozone concentrating stage.
[Ozone Generating Stage]
[0053] In the ozone producing stage, ozone is produced by the ozone
generator 27 which is an example of an ozone generation unit
configured to generate ozone. The ozone generator 27 may be any
device as long as an ozone gas is generated therein, and examples
include a device which produces ozone by electrical discharge using
oxygen or air as a raw material.
[Ozone Concentrating Stage]
[0054] In the ozone concentrating stage, ozone produced in the
ozone generator 27 is concentrated and stored in the ozone
concentrator 28. The ozone concentrator 28 may be any device as
long as ozone can be concentrated and stored therein, and examples
include a device using a container filled with a silica gel as an
ozone adsorbent in which ozone absorbed can be desorbed and
released by changing the pressure or temperature in the
container.
[0055] The ozone concentrated in the ozone concentrating stage is
released from the ozone concentrator 28 in an ozone injecting and
circulating stage described later and used for decomposing the
microorganisms.
[0056] The ozone generating stage and the ozone concentrating stage
described above are conducted in this order at every release of
ozone from the ozone concentrator, and a state with ozone stored is
always maintained in the ozone concentrator 28.
[0057] Hereinunder, a sludge transferring stage, an ozone treatment
stage, and a treated sludge returning stage will be shown. The
stages are conducted in this order, and a batch treatment is
carried out with the three stages as one cycle. That is, after the
three stages are performed in this order and the treated sludge
returning stage is completed, the sludge transferring stage is
started.
[0058] A downtime may be optionally provided between the completion
of the treated sludge returning stage and the start of the sludge
transferring stage to intermittently perform the above three
stages.
<Sludge Transferring Stage>
[0059] While performing the biological treatment stage and the
ozone gas producing stage, the sludge transferring stage is
started.
[0060] In the sludge transferring stage, the valve 46 is opened and
a part of the microorganism-mixed liquid 7 stored in the aeration
tank 1 is sucked through the sludge transferring pipe 15 by the
sludge transferring pump 18, and transferred into the ozone
reaction tank 14 which is an example of the ozone reaction unit
according to the present invention. At this time, the valve 48
provided on the sludge extracting pipe 16 is in a closed state so
that the microorganism-mixed liquid 7 does not flow out from the
ozone reaction tank 14 and a predetermined amount of sludge is
transferred into the ozone reaction tank 14. The combination of the
valve 46, the sludge transferring pipe 15, and the sludge
transferring pump 18 is one example of the withdrawing unit
configured to withdraw a partial water from the water treated by
the microorganism treatment unit.
[0061] The amount of sludge transferred may be controlled by the
operation time of the sludge transferring pump 18, may be
controlled by providing an integrating flowmeter on the sludge
transferring pipe 15 to check the amount of the sludge flowing
through the pipe, or may be controlled by providing a level sensor
in the ozone reaction tank 14 to stop the transfer when a
predetermined water level is reached.
<Ozone Treatment Stage>
[0062] In the water treatment system according to the present
invention, the reduction in the amount of excess sludge generated
is achieved through decomposition of microorganisms by ozone. In
order to efficiently bring the microorganisms into contact with
ozone, the ozone treatment stage includes two stages of the ozone
injecting and circulating stage and a sludge concentrating stage
described below, and the stages for predetermined times are
repeatedly carried out.
[Ozone Injecting and Circulating Stage]
[0063] In the ozone injecting and circulating stage, the valve 48
on the sludge extracting pipe 16, and the valve 47 on the sludge
circulating pipe 20 are opened, whereas the valve 46 on the sludge
transferring pipe 15 is closed. The microorganism-mixed liquid 7 in
the ozone reaction tank 14 is withdrawn from the sludge extracting
pipe 16 by the sludge circulating pump 19 and fed into the sludge
circulating pipe 20.
[0064] When the microorganism-mixed liquid 7 passes through the
ejector 23 placed on the sludge circulating pipe 20, an ozone gas
stored in the ozone concentrator 28 is released from the ozone
concentrator 28, the microorganism-mixed liquid 7 comes into
contact with the ozone gas, and excessively grown microorganisms
present in the microorganism-mixed liquid 7 are decomposed by
ozone.
[0065] As a method of injecting ozone, for example, a method in
which an air diffuser is provided in the ozone reaction tank 14 and
ozone is released from the air diffuser may be adopted, but a
method using a venturi device such as an ejector is more preferred
since the efficiency of ozone absorption is higher and a more
efficient sludge reduction can be achieved with a small amount of
ozone.
[0066] Here, the efficiency of ozone dissolution into the
microorganism-mixed liquid depends greatly on the ratio of the
ozone gas flow rate to the microorganism-mixed liquid flow rate in
the ejector 23, the smaller the proportion of the ozone gas flow
rate, the more efficiently the ozone can be dissolved. Accordingly,
the ratio (g/L) of the ozone gas flow rate to the
microorganism-mixed liquid flow rate in the ejector 23 may be 0.05
to 0.4, and preferably 0.1 to 0.3.
[0067] By concentrating an ozone gas by the ozone concentrator 28
in the ozone gas producing stage as in the Embodiment, an ozone gas
having an extremely high concentration of approximately from 1000
to 2000 mg/NL can be obtained, and it becomes possible to quickly
complete the reaction of ozone with the microorganisms. However, it
is not necessarily possible to obtain the effect of the invention
of the present application only with the high concentrated ozone as
above. That is, the effect of the invention of the present
application can also be obtained by, for example, in the ozone gas
producing stage, directly injecting an ozone gas of approximately
100 mg/NL generated in an ozone generator into the
microorganism-mixed liquid 7 without ozone concentration.
[Sludge Concentrating Stage]
[0068] In the sludge concentrating stage, the microorganism-mixed
liquid 7 flowing through the sludge circulating pipe 20 flows via
the sludge introducing pipe 22 into the ozone reaction tank 14. The
sludge introducing pipe 22 has been inserted into the central area
of the ozone reaction tank 14, and the introduced
microorganism-mixed liquid 7 is ejected downwardly in the vertical
direction from the central area of the ozone reaction tank 14.
[0069] The ejected microorganism-mixed liquid is sprayed onto the
baffle plate 30 placed below the outlet port of the sludge
introducing pipe 22, and the microorganism-mixed liquid flow is
changed in the flow direction into the horizontal direction. The
baffle plate 30 is placed inside a guide pipe 31 of a hollow
cylinder as shown in FIG. 2 or a rectangular parallelepiped as
shown in FIG. 3a. Thus, a microorganism-mixed liquid flow 34 is
changed in the flow direction upwardly by an inner wall of the
guide pipe 31, and runs upwardly along the inner wall of the guide
pipe 31 in the central area of the ozone reaction tank. That is,
the combination of the baffle plate 30 and the inner wall of the
guide pipe 31 is one example of the moving means according to the
present invention.
[0070] The flow regulator 32 is placed above the guide pipe 31, and
the microorganism-mixed liquid flow 34 is regulated in the course
of the upward passing through the flow regulator 32.
[0071] Examples of the structure of the flow regulator 32 include a
structure as shown in FIG. 4 in which plates (referred to as flow
regulating plates) are arranged adjacently each other over a
horizontal cross section of the ozone reaction tank, and a
structure as shown in FIG. 5 in which cylinders (referred to as
flow regulating cylinders) are arranged adjacently each other
throughout a horizontal cross section of the ozone reaction tank.
Incidentally, FIG. 4 shows flow regulating plates 35, and FIG. 5
shows flow regulating cylinders 36. FIG. 6 shows a horizontal cross
section in a case where the flow regulating plates 35 are used as a
flow regulator and the ozone reaction tank 14 of a circular shape
is used, and FIG. 7 shows a horizontal cross section in a case
where a rectangular-shaped water tank is used.
[0072] As described above, since upward flow occurs in the central
area of the ozone reaction tank 14, on the outer periphery of the
ozone reaction tank 14, that is, the outside of the baffle plate,
downward flow as shown in FIG. 5 occurs. In the downward flow, by a
flow regulation effect, when the flow passes through the flow
regulator 32 downwardly from above, a mild flow without turbulence
is formed below the flow regulator 32.
[0073] In the course of the upward flowing through the guide pipe,
the microorganism-mixed liquid flow 34 is vigorously turbulent.
However, as described above, since the turbulence is suppressed by
the flow regulator 32, solid matter, that is, the microorganisms,
contained in the microorganism-mixed liquid 7, becomes likely to
settle by its own weight. This allows the solid matter in the
microorganism-mixed liquid, that is, the undecomposed
microorganisms, to settle at a site outside the baffle plate where
the flow is mild, and the undecomposed microorganisms settle and
are concentrated on the bottom of the ozone reaction tank 14. That
is, the flow regulator 32 is one example of the flow regulation
means according to the present invention.
[0074] For achieving the flow regulation effect by the flow
regulator 32 as described above, for example, in the case where the
flow regulating plates as shown in FIG. 4 are used, an excessively
large interval between plates is not preferred. Also, an
excessively small interval causes clogging between the flow
regulating plates with the solid matter contained in the
microorganism-mixed liquid 7 and the flow regulation effect is
impaired. Accordingly, a suitable interval may be made such that
the proportion of the horizontal cross sectional area of the spaces
between flow regulating plates relative to the horizontal cross
sectional area of the ozone reaction tank 14 is 10 to 50%, and
preferably 10 to 40%, and the plural flow regulating plates are
preferably disposed at an equal interval. In addition, the same is
applied in the flow regulating cylinders as shown in FIG. 5, and it
is preferred that the cylinders having an equal cross sectional
area are arranged throughout a horizontal cross section of the
ozone reaction tank 14 so that the proportion of the cross
sectional area of the hollow portions in the cylinders relative to
the horizontal cross sectional area of the ozone reaction tank 14
is 10 to 50%, and preferably 10 to 40.
[0075] Incidentally, the proportion of the horizontal cross
sectional area of the spaces between the flow regulating plates, or
the hollow portions of the flow regulating cylinders, that is, the
hatched area shown in FIG. 9, relative to the horizontal cross
sectional area of the ozone reaction tank 14 is referred to as an
"aperture ratio".
[0076] Furthermore, the flow regulating plates and the flow
regulating cylinders shown in FIG. 4 and FIG. 5 may be inclined at
an angle with respect to the vertical direction. When an angle
.theta., that is, an angle shown in FIG. 10, is excessively large,
the solid matter is likely to accumulate on the inclined plates or
on the inclined cylinders and may cause clogging of the flow path
or damage of the apparatus. Accordingly, the inclination angle with
respect to the vertical direction may be 0 to 60 degrees, and
preferably 0 to 50 degrees.
[0077] The present invention is characterized by repeatedly
performing the ozone injecting and circulating stage and the sludge
concentrating stage of predetermined times. Accordingly, in the
sludge concentrating stage, the solid matter in the
microorganism-mixed liquid 7 accumulating on the bottom of the
ozone reaction tank 14, that is, the undecomposed microorganisms,
is withdrawn via the sludge extracting pipe 16 by the sludge
circulating pump 19, and introduced again into the sludge
circulating pipe 20 and comes into contact with ozone.
[0078] The remaining ozone that has not been consumed by the
reaction among the ozone injected as described above is transferred
into an ozone decomposer (not shown) via the ozone releasing path
17 as an exhaust gas, detoxified therein and dissipated into the
atmosphere.
<Method and Conditions for Operation>
[0079] Hereinunder, conditions for performing the ozone treatment
stage for achieving the maximum effect of the present invention
will be described.
[Amount of Ozone Injected]
[0080] In the configuration of the present invention, an amount of
ozone required for dissolving microorganisms in a
microorganism-mixed liquid (an amount required for one ozone
treatment stage) is obtained with the following expression,
according to the intensive study of the inventors of the present
application.
[O.sub.3 dosage]={[MLSS].times..alpha.}.times.[V].times..beta.
Expression 1
[O.sub.3 dosage]: amount of injected ozone required
(mgO.sub.3/time) [MLSS]: solid matter concentration in aeration
tank (g/L) [V]: amount of microorganism-mixed liquid treated at one
time (L/time) .alpha.: MLSS/MLVSS ratio .beta.: amount of ozone
required for MLVSS decomposition (mgO.sub.3/gMLVSS)
[0081] .alpha. indicates a ratio of the amount of solid matter
derived from microorganisms (MLVSS) in the solid matter
concentration in the aeration tank (MLSS), and is generally 0.4 to
0.7 although it varies for each wastewater. .beta. indicates an
amount of ozone required for decomposing a unit amount of MLVSS,
and is from 20 to 70 mgO.sub.3/gMLVSS according to the study of the
present inventors. .beta. is from 30 to 60 mgO.sub.3/gMLVSS in many
cases, and preferably set in this range.
[0082] [MLSS] can be obtained by measuring MLSS in the aeration
tank, and [V] is determined by arbitrarily regulating the amount of
the microorganism-mixed liquid transferred from the aeration tank
to the ozone reaction tank 14. Since it is not preferred that the
volume of the ozone reaction tank is excessively large, [MLSS] may
desirably be 0.1 to 7%, and preferably 0.2 to 5% based on the
aeration tank volume. [A] may be determined by sampling and
analysis of the microorganism-mixed liquid performed by a system
manager as the need arises, or may be determined by using a
measurement value of an MLSS concentration meter which is
previously placed in the aeration tank.
[Number of Times of Ozone Treatment Stage Performed Per Day]
[0083] In the water treatment system according to Embodiment 1,
microorganisms are decomposed by ozone, a liquid after the ozone
treatment is returned to the aeration tank, and organic substances
contained in the liquid is allowed to be utilized by
microorganisms, thereby reducing sludge. It is the relation: "the
amount of microorganisms decomposed by ozone.noteq.the amount of
sludge reduced" that is to be considered here. In other words,
since the microorganisms in the aeration tank utilize the
decomposed microorganisms contained in the liquid after the ozone
treatment to perform new production, new microorganisms are
generated in the aeration tank. However, the amount of the
microorganisms generated is smaller than the amount of the
microorganisms decomposed by ozone treatment, resulting in
achieving reduction of sludge.
[0084] Owing to the complicated relation, in order to fully
achieving the effect of the excess sludge reduction by ozone
according to the present invention, it is desired, in addition to
that ozone is injected in the amount calculated by Expression 1,
that the amount of the microorganism-mixed liquid treated at one
time ([V] in Expression 1) and the number of times of the ozone
treatment stage performed per day [F] are set so as to give a
"treated sludge ratio" of 1.5 to 6, preferably 2 to 5.
[0085] Here, the treated sludge ratio refers to a ratio of an
amount of sludge subjected to the ozone treatment per day relative
to an amount of excess sludge per day generated without the ozone
treatment, and calculated by the following expression.
[R]=[Q1]/[Q2] Expression 2
[R]: treated sludge ratio [Q1]: amount of sludge subjected to ozone
treatment per day (gMLSS/day) [Q2]: amount of excess sludge per day
(gMLSS/day)
[0086] [Q1] is an MLSS weight that is subjected to the ozone
treatment per day, and calculated as the product of the solid
matter concentration in the aeration tank ([SS] in Expression 1),
the amount of the microorganism-mixed liquid treated at one time
([V] in Expression 1), and the number of times of the ozone
treatment stage performed per day. Accordingly, [Q1] is as
follows.
[Q1]=[MLSS].times.[V].times.[F] Expression 3
[Q1]: amount of sludge subjected to ozone treatment per day
(gMLSS/day) [MLSS]: solid matter concentration in aeration tank
(g/L) [V]: amount of microorganism-mixed liquid treated at one time
(L/time) [F]: number of times of ozone treatment stage performed
per day (times/day)
[0087] [Q2] refers to the weight of excess sludge generated without
the ozone treatment as described above. [Q2] may be calculated in
advance from results of daily measurement of the solid matter
concentration in the aeration tank before starting the excess
sludge reduction by ozone according to the present invention, or
may be calculated by the following expression even after applying
the present invention.
[Q2]={{[BOD.sub.in]-[BOD.sub.out].times..gamma.+{[SS.sub.in]-[SS.sub.out-
]}}.times.[W] Expression 4
[Q2]: amount of excess sludge per day (gMLSS/day) [BOD.sub.in]: BOD
contained in wastewater (g/L) [BOD.sub.out]: BOD contained in
treated water (g/L) [W]: amount of wastewater flowing-in per day
(L/D) .gamma.: sludge conversion [SS.sub.in]: solid matter
concentration in wastewater (g/L) [SS.sub.out]: solid matter
concentration in treated water (g/L)
[0088] Here, BOD is a biological oxygen demand, and a measure of an
amount of organic substances contained in water. .gamma. is a
sludge conversion, that is, a proportion of organic substances that
are converted to microorganisms in flowing-in organic substances,
and is generally 0.1 to 0.4. [SS.sub.in] and [SS.sub.out] are solid
matter concentrations in a flowing-in wastewater and a flowing-out
treated water, respectively.
[0089] From the foregoing, the number of times of the ozone
treatment stage performed per day [F] can be obtained by the
following expression.
[F]={[R].times.[Q2]}/{[MLSS].times.[V]} Expression 5
[F]: number of times of ozone treatment stage performed per day
(times/day) [R]: treated sludge ratio [Q2]: amount of excess sludge
per day (gMLSS/day) [MLSS]: solid matter concentration in aeration
tank (g/L) [V]: amount of microorganism-mixed liquid treated at one
time (L/time)
[0090] Accordingly, it is desired that the number of times of the
ozone treatment stage calculated as above are performed in a manner
that the intervals of the performances are equal.
[Time Period of Ozone Treatment Stage]
[0091] The time period of the ozone treatment stage [T1] has to be
such a time period that allows the number of times calculated by
Expression 5 as described above to be performed in one day. In
addition, [T1] has to be such a time period that allows all the
microorganism-mixed liquid stored in the ozone reaction tank to
pass through the ejector to come into contact with ozone gas.
Furthermore, [T1] has to be such a time period that allows the
[O.sub.3 dosage] calculated in Expression 1 mentioned above to be
injected.
[0092] Accordingly, the time period of the ozone treatment stage
[T1] is desirably set so as to simultaneously satisfy the following
three expressions.
[T1]+[T2]+[T3].ltoreq.24 (h/day)/[F] Expression 6
[T1].gtoreq.[V]/[C] Expression 7
[O.sub.3 dosage]=[O.sub.3 conc].times.[O.sub.3 flow].times.[T1]
Expression 8
[T1]: time period of ozone treatment stage (h/time) [T2]: sum of
time period of sludge transferring stage and time period of treated
sludge returning stage (h/time) [T3]: downtime (h/time) [F]: number
of times of ozone treatment stage performed per day (times/day)
[V]: amount of microorganism-mixed liquid treated at one time
(L/time) [C]: sludge circulating pump flow rate (L/h) [O.sub.3
dosage]: amount of injected ozone required (GO.sub.3/time) [O.sub.3
conc]: ozone gas concentration (GO.sub.3/L) [O.sub.3 flow]: ozone
gas flow rate (L/h)
[0093] [T2] indicates a sum of the time period of the sludge
transferring stage and the time period of the treated sludge
returning stage described later (hereinafter, referred to as
miscellaneous time). [T3] refers to a "downtime" where none of the
sludge transferring stage, the ozone treatment stage, and the
treated sludge returning stage is performed. In the present
invention, the sludge transferring stage, the ozone treatment
stage, and the treated sludge returning stage are performed in this
order. Since the three stages are performed as one cycle and
downtimes are provided between the cycles, a relation of Expression
6 has to be satisfied. [T2] and [T3] can be arbitrarily set, and,
for example, [T2] may be 10 to 120 minutes, preferably 10 to 60
minutes, and [T3] may be 0 to 12 hours, preferably 3 to 12
hours.
[0094] As described above, [V] is 0.1 to 7%, and preferably 0.2 to
5% relative to the aeration tank volume. As described above, the
ozone gas flow rate [O.sub.3 flow] and the sludge circulating pump
flow rate [C] are desirably set so as to satisfy g/L in the ejector
of 0.05 to 0.4, preferably 0.1 to 0.3. The ozone gas concentration
[O.sub.3 conc] may be arbitrarily regulated in the range of 0.05G
to 2 g/L, and preferably 0.1 to 2 g/L.
[0095] Under the above conditions, [T1] may be arbitrarily set.
[0096] Although the number of times of ozone treatment stage
performed per day [F] and the time period of ozone treatment stage
[T1] can be arbitrarily regulated as described above, it is not
preferred that the ozone treatment is performed too frequently.
This is because a slight amount of unreacted ozone, which remains
in the microorganism-mixed liquid that has been treated with ozone,
frequently flows in the aeration tank, then impairing the activity
of the microorganism in the aeration tank to deteriorate the
performance of the wastewater treatment.
[0097] Consequently, [F] is desirably set so that the sum of [T1],
[T2], and [T3] is 30% or more, and preferably 40% or more relative
to HRT (hydraulic retention time) of the aeration tank.
[0098] Based on the above description, in the present invention, it
is possible to always allow the liquid in contact with ozone to
contain undecomposed microorganisms at a high concentration, and by
optimizing the amount of ozone injected, it is possible to allow
undecomposed microorganisms to efficiently react with ozone.
[0099] <Treated Liquid Returning Stage>
[0100] After the ozone treatment stage is completed, the valve 47
on the sludge circulating pipe 20 is closed, whereas the valve 49
on the treated liquid returning pipe 21 is opened, and the
microorganism-mixed liquid 7 after the ozone treatment stored in
the ozone reaction tank is returned into the aeration tank 1. The
microorganism-mixed liquid after the ozone treatment contains
residue of the microorganism decomposed by ozone. The
microorganisms in the aeration tank decompose and utilize the
residue as a substrate, and the residue is dissipated into the air
as carbon dioxide gas, thereby achieving the sludge reduction.
[0101] The sludge transferring stage, the ozone treatment stage,
and the treated liquid returning stage described above, are
conducted while the biological treatment stage and the ozone gas
producing stage are performed, and are not started after the
biological treatment stage and the ozone gas producing stage are
stopped.
Embodiment 2
[0102] FIG. 11 shows an example of the configuration of the
apparatus of the present invention in the case where a
"conventional activated sludge process" is applied in the
biological treatment stage.
[0103] In FIG. 11, the sludge transferring pipe 15 is connected to
the sludge returning pipe 12. In FIG. 7, the sludge transferring
pump 18 is not provided. The configuration is the same as in FIG. 1
except for the above points.
[0104] In Embodiment 2, the separated sludge 33 accumulated on the
sedimentation tank 5, that is, the microorganisms flowing out from
the aeration tank 1 is transferred to the ozone reaction tank 14
and subjected to an ozone treatment. When the sludge transferring
stage is started, the valve 46 on the sludge transferring pipe 15
is opened, and the microorganism-mixed liquid 7 flowing through the
sludge returning pipe 12 is transferred through the sludge
transferring pipe 15 into the ozone reaction tank 14.
[0105] The transfer amount may be controlled by the same method as
in Embodiment 1. Other operations than the above are the same as in
Embodiment 1. In addition, the operation conditions, such as the
amount of ozone injected [O.sub.3 dosage], the number of times of
the ozone treatment stage performed per day [F], and the time
period of the ozone treatment stage [T1], may be calculated by the
expressions with the "solid matter concentration in the separated
sludge (g/L)" substituted for "MLSS", and the "amount of the
separated sludge treated at one time (L/time)" substituted for
[V].
Embodiment 3
[0106] FIG. 12 shows an example of the configuration of the
apparatus of the present invention in the case where a "biological
membrane process" is applied in the biological treatment stage. In
FIG. 12, microorganism carriers 37 are put in the aeration tank 1.
The configuration is the same as in FIG. 11 (Embodiment 2) except
for the above point.
[0107] The microorganism carriers put in the aeration tank are
intended to have microorganisms deposited on the surface thereof to
maintain the amount of organics in the aeration tank at a high
level, and such a biological treatment technique is generally
called "biological membrane process". In the case where no carrier
is put in the aeration tank, that is, the case of the "conventional
activated sludge process" described in Embodiment 1, the floating
microorganisms are allowed to utilize organic substances in a
wastewater to purify the wastewater, whereas the biological
membrane process is different in that purification is performed by
microorganisms deposited and immobilized on carrier surfaces.
However, the processes share a common point that they are
wastewater purification by microorganisms. Also in the biological
membrane process, a liquid containing microorganisms has to be
allowed to flow out into the subsequent sedimentation tank for a
solid-liquid separation, and the separated sludge has to be
discarded as excess sludge. Accordingly, in the case where the
biological membrane process is used in the biological treatment
stage, the configuration in FIG. 12 is adopted and a part or all of
the separated sludge 33 accumulating in the sedimentation tank 5 is
transferred to the ozone treatment stage.
[0108] In addition, FIG. 12 illustrates a "fluid bed type" where
sponge carriers or the like are placed, but a "fixed bed type"
where the aeration tank is charged with a plastic filler as shown
in FIG. 13 may be adopted.
[0109] In any configuration of FIG. 12 and FIG. 13, the operation
is the same as in Embodiment 2.
[0110] Incidentally, in Embodiments 1 to 3, a sedimentation tank
provided as a subsequent stage of the aeration tank is used as a
solid-liquid separation device, but any device may be used as long
as it has such a configuration that can perform solid-liquid
separation and can transfer the separated sludge to the ozone
treatment stage, and, for example, a floatation separation device
and a centrifugal separation device may be used in place of the
sedimentation tank.
Embodiment 4
[0111] FIG. 14 shows a configuration of Embodiment 4. Embodiment 4
is an example of the configuration of the case where the "membrane
bioreactor process (MBR)" is applied in the biological treatment
stage.
[0112] A water treatment system in FIG. 14 includes the
solid-liquid separation membrane 38, a filtrate suction pipe 39, a
filtering pump 40, and a filtrate transferring pipe 41. In
Embodiment 4, the sludge withdrawing pipe 10 is connected to the
aeration tank 1. Since Embodiment 4 uses MBR, a solid-liquid
separation means such as the sedimentation tank 5 does not have to
be provided as a subsequent stage of the aeration tank. The
configuration is the same as in FIG. 1 (Embodiment 1) except for
the above points.
[0113] MBR shown in FIG. 14 is called "immersion-type MBR" since a
solid-liquid separation membrane is immersed in the aeration tank.
As with the case of the "conventional activated sludge process"
shown in Embodiment 1, the immersion-type MBR is a process in which
microorganisms floating in the aeration tank are allowed to utilize
organic substances in a wastewater to remove the organic substances
in the wastewater, and a microorganism-mixed liquid is subjected to
solid-liquid separation with a solid-liquid separation membrane
placed in the aeration tank, thereby obtaining a clear treated
water. As compared with a conventional activated sludge process and
the like, it is possible to reduce the space of the equipment and
to enhance the quality of the treated water. MBR shares a common
point that it is wastewater purification by microorganisms. Excess
sludge, which is generated, is required to be discharged and
discarded.
[0114] As described above, since the immersion-type MBR is the same
as the "conventional activated sludge process" except that a
solid-liquid separation is performed with a membrane which is
immersed in the aeration tank 1, a microorganism-mixed liquid is
withdrawn from the aeration tank, and then subjected to an ozone
treatment, whereby the effect of the present invention can be
achieved, as with the case of Embodiment 1.
[0115] Although FIG. 14 shows a configuration of the case where an
immersion-type MBR is applied in the biological treatment stage,
for example, as shown in FIG. 15 or 16, a solid-liquid separation
membrane may be provided outside the tank. Specifically, as shown
in an example shown in FIG. 15, a membrane separation tank 41
having the solid-liquid separation membrane 38 placed therein may
be provided, or as shown in an example shown in FIG. 16, a membrane
water-feeding path 43, a membrane water-feeding pump 44, and a
concentrated sludge retuning path 45 may be provided to place the
solid-liquid separation membrane 38 outside the tank.
Embodiment 5
[0116] FIG. 17 shows another embodiment, Embodiment 5 of the
present invention. As with the case of Embodiment 4, Embodiment 5
is an example of the case where the present invention is applied to
MBR, and ozone produced in the ozone production device 24 is used
for washing the solid-liquid separation membrane 38.
[0117] The solid-liquid separation membrane 38 filters under
reduced pressure a microorganism-mixed liquid in the aeration tank
1 by driving the filtering pump 40. As the pressure inside the
filtrate suction pipe 39 decreases (that is, as the transmembrane
pressure difference increases), the solid-liquid separation
membrane 38 is required to be washed. Although the membrane is
typically washed with hypochlorous acid, in this embodiment,
washing with ozone water which has a stronger washing effect is
possible.
[0118] In FIG. 17, in addition to the configuration in FIG. 14, an
ozone injecting branched path 53, an ozone water production unit
54, a treated water returning path 55, an ozone water transferring
path 56, an ozone water feeding pump 57, and valves 70, 71 are
provided.
[0119] After an increase in the transmembrane pressure difference
is detected as described above, an ozone water producing stage is
started. In an ozone water washing stage, the valve 71 is opened,
and an ozone gas concentrated by the ozone concentrator 28 is fed
via the ozone injecting branched path 53 connected to the ozone
injecting path 26 to the ozone water production unit. On the other
hand, a treated water returning path 55 is connected to the ozone
water production unit 54, and a part of the treated water treated
in the biological treatment stage and released is returned to the
ozone water production unit. The aforementioned ozone gas comes in
contact with the treated water in the ozone water production unit
54 to produce an ozone water.
[0120] As a configuration of the ozone water production unit, for
example, those shown in FIG. 18 and FIG. 19 are exemplified. The
ozone water production unit illustrated in FIG. 18 includes an
ozone gas diffuser 58, an ozone water tank 59, and a treated water
60. An ozone gas introduced through the ozone gas injecting
branched path 53 is dissipated from the ozone gas diffuser 58, and
ozone is dissolved in the treated water 60 received in the ozone
water tank 59, thereby producing an ozone water.
[0121] An ozone water production unit illustrated in FIG. 19
includes an ozone water circulating pump 61, an ozone water
producing ejector 62, and an ozone water circulating pipe 63.
Flowmeters 68 and 69 are placed on the ozone injecting branched
path 53 and the ozone water circulating pipe 63, respectively. The
treated water 60 received in the ozone water tank flows through the
ozone water circulating pipe 63 by the ozone water circulating pump
61. On the other hand, the ozone water producing ejector 62 is
placed on the ozone water circulating pipe 63, and also connected
to the ozone injecting branched path 53. The treated water 60 flows
through the ozone water circulating pipe, and in the course of
passing through the ozone water producing ejector 62, absorbs a
high-concentration ozone gas via the ozone injecting branched path
53, and comes in contact with ozone, thereby producing an ozone
water. An ozone gas flow rate and an ozone water circulating
pump-ejecting flow rate are desirably regulated so that g/L in the
ozone water producing ejector 62 is also 0.1 to 0.3.
[0122] The time period required for the ozone water production
depends on the ozone gas concentration, but, for example, when
using an approximately 300 mgO.sub.3/NL ozone gas, the gas is
desirably diffused or circulated for a time period between 5 and 60
minutes. As a result, the ozone water of at least 60 mgO.sub.3/L or
more in terms of a concentration of the dissolved ozone can be
produced. When the ozone gas concentration is made higher, the
ozone water concentration can also be made higher.
[0123] As described above, the ozone water producing stage is
started by detecting an increase in the transmembrane pressure
difference, and when the ozone water producing stage is completed,
the process proceeds to the membrane washing stage.
[0124] In the membrane washing stage, the ozone water produced in
the ozone water production unit 54 is injected into the secondary
side of the solid-liquid separation membrane through the ozone
water transferring path 56 by the ozone water feeding pump 57. At
this time, the valve 64 is opened and the valve 65 is closed. The
filtering pump 40 is out of operation and the filtration under
reduced pressure with the solid-liquid separation membrane 38 is in
a resting state.
[0125] Although the amount of washing water and the time period of
washing depend on the ozone water concentration used for the
washing, for example, when an ozone water of approximately 60
mgO.sub.3/L in terms of the concentration of the dissolved ozone is
used for the washing, it is sufficient that the amount of washing
water is 0.5 to 5 L/m.sup.2, preferably 0.5 to 3 L/m.sup.2 per unit
membrane area of the solid-liquid separation membrane 38, and that
the time period of washing is 5 to 120 minutes, preferably 5 to 90
minutes.
[0126] When the washing with the ozone water is completed, by
stopping the ozone water feeding pump 57, opening the valve 65,
closing the valve 64, and driving again the filtering pump 40, the
filtration of the microorganism-mixed liquid 7 under reduced
pressure is restarted.
[0127] Incidentally, the ozone water producing stage and the
membrane washing stage described above can be performed at the same
time with the ozone treatment stage of sludge, and when the stages
are performed at the same time, the valve 70 is opened, and the
ozone gas released from the ozone concentrator 28 is fed to both of
the ozone water production unit 54 and the ejector 23.
[0128] Other operations are the same as in Embodiment 4.
[0129] In addition, a process in which an ozone water is produced
to be used for washing a solid-liquid separation membrane as
described in this embodiment can be applied to MBR, for example,
having a form as shown in FIGS. 15 and 16.
EXAMPLES
[0130] In the apparatus having a configuration of FIG. 14, the
effect of the present invention is shown based on a test of
wastewater treatment.
[0131] An artificial sewage was used as a test water. Therefore,
the properties of the wastewater and the amount of the treated
water were always constant. In Examples 1 and 2, sludge was
appropriately discharged from an aeration tank to maintain the MLSS
concentration and the MLVSS/MLSS ratio constant. Incidentally,
details of the properties of the wastewater and the conditions of
the test apparatus are shown in Table 1 and Table 2. An inclined
plates were used as a flow regulator.
TABLE-US-00001 TABLE 1 It is a table for explaining conditions of
experiments for verifying the effect of the present invention.
Properties pH 7.5 of BOD 200 mg/L wastewater T-SS 100 mg/L
Conditions Amount of treated water 5000 L/D of test Aeration tank
2000 L apparatus Volume of ozone reaction tank 72 L ([V] Amount of
microorganism-mixed liquid treated at one time) MLSS 6900 mg/L
MLVSS 2760 mg/L [Q1] Amount of excess sludge generated 850
qMLSS/day
TABLE-US-00002 TABLE 2 It is a table for explaining conditions of
experiments for verifying the effect of the present invention.
Conditions of [O3 conc] Ozone gas concentration 200 mg/L ozone
treatment [O3 flow] Ozone gas flow rate 49.7 L/h (Example 1) [C]
Sludge circulation pump flow rate 184 L/h G/L 0.27 [.alpha.]
MLSS/MLVSS ratio 0.4
Example 1
[0132] Example 1 shows results of ozone treatments of a
microorganism-mixed liquid conducted while varying the flow
regulating plate interval, that is, the aperture ratio. However,
the flow regulating plate intervals were equal.
[Test Method]
[0133] In Example 1, the verification was conducted by a method in
which while performing a biological treatment stage, an ozone
treatment stage was started and stopped at an arbitrarily
timing.
[0134] The microorganism-mixed liquid in the ozone reaction tank
was sampled at every fixed time from the start of the ozone
treatment stage, and subjected to an MLVSS concentration
measurement. From the results, a time period required for
completely decomposing MLVSS was grasped. From the time period, the
amount (weight) of ozone fed during the time period was
calculated.
[0135] The above operation was conducted for each aperture ratio
and the amounts of ozone fed were compared among the aperture
ratios. Incidentally, the angle .theta. of the inclined plates with
respect to the vertical direction was 45 degrees. The conditions
for the ozone treatment, such as the ozone concentration, are shown
in Table 2.
[Results]
[0136] FIG. 12 shows the relation between the aperture ratio and
the value obtained by dividing the amount of ozone fed by the
amount of MLVSS decomposed, that is, the amount of ozone required
for decomposition per unit MLVSS.
[0137] It is apparent from FIG. 12 that, with an aperture ratio of
10 to 50%, the weight of ozone required for decomposition was 30 to
59 mgO.sub.3/gMLVSS per unit MLVSS weight, but when the aperture
ratio exceeded 50%, the weight of ozone rapidly increased and the
efficiency of decomposition deteriorated. This indicates that as
the interval between flow regulating plates increases, the flow
regulation effect is reduced and it becomes difficult to separate
and concentrate the undecomposed microorganisms and the
microorganisms and organic substances. Thus, ozone is consumed by
other organic substances than the microorganisms, resulting in
deterioration in the efficiency of decomposing microorganism.
[0138] In FIG. 20, the 100% aperture ratio represents a
configuration including no flow regulator. That is, it shows a
configuration of a conventional wastewater treatment system.
[0139] When the aperture ratio was less than 10%, the flow paths
between the inclined plates were clogged with the microorganisms,
and the flow regulation effect could not be obtained so that the
separation and concentration of the undecomposed microorganism
could not be achieved.
[0140] From the foregoing, it was demonstrated that the aperture
ratio is suitably 10 to 50%, and that sludge can be decomposed with
a clearly smaller amount of ozone fed than that in the conventional
apparatus.
Example 2
[0141] In Example 2, an ozone treatment was conducted using
inclined plates as a flow regulator as with the case of Example 1,
while varying the inclination angle .theta. of the inclined plates
with respect to the vertical direction. However, the aperture ratio
was fixed to 30%.
[0142] Also in Example 2, the verification was conducted by a
method in which an ozone treatment stage was started and stopped at
an arbitrarily time as with the case of Example 1. The conditions
for the ozone treatment were the same as in Example 1 and shown in
Table 2.
[0143] The results are shown in Table 3. When the angle was larger
than 60 degrees, solid matter accumulated on the flow regulator or
between the inclined plates, and the paths between the inclined
plates were clogged. For this reason, the flow regulation effect in
the flow regulator could not be obtained, and separation and
concentration of the undecomposed microorganism could not be
achieved. From the foregoing, it was demonstrated that the
inclination angle of the inclined plates with respect to the
vertical direction is suitably 0 to 60 degrees.
TABLE-US-00003 TABLE 3 It is a table for explaining the
verification results of the flow regulator structure in the present
invention. Angle of inclined plates (degree) 0 20 50 60 70 80
Occurrence of clogging No No No No Yes Yes
Example 3
[0144] In Example 3, verification was conducted for the excess
sludge reduction effect and the wastewater treatment performance,
by carrying out a continuous treatment for 40 days after completion
of the verification in Example 1 and 2.
[0145] During the test period, as shown in Table 4, the treatment
conditions was varied at every 10 days, and the respective treated
water qualities in the conditions were compared. Also in this
Example, the artificial sewage shown in Table 1 was used as a
wastewater.
TABLE-US-00004 TABLE 4 It is a table for explaining the conditions
of a test for verifying the effect of the present invention. 0 to
10 11 to 20 21 to 30 31 to 40 Experiment period days days days days
Ozone treatment No Yes Yes Yes Flow regulator No Yes No No Ratio of
ozone injection amount -- 1 1 2.4
Period 1
[0146] In Period 1, no ozone treatment, but only a biological
treatment stage was performed. Withdrawal from an aeration tank was
appropriately performed to maintain the MLSS concentration in the
aeration tank constant.
[0147] In Period 1, the treated water quality was stable, and the
BOD removal ratio was generally approximately 95% over the period
(FIG. 21). In addition, the amount of sludge discharged per day was
approximately 850 gMLSS/day.
Period 2
[0148] In Period 2, an ozone treatment was started with the present
invention applied. The conditions for the flow regulator and the
ozone treatment are shown in Table 5. Also in Period 2, the MLSS
concentration in the aeration tank was maintained constant.
TABLE-US-00005 TABLE 5 It is a table for explaining the conditions
of the experiments for verifying the effect of the present
invention. Conditions of Types Inclined plates flow regulator
Aperture ratio 30% .theta. 45 degrees Conditions of [O3 conc] Ozone
gas 200 mg/L ozone concentration treatment [O3 flow] Ozone gas flow
rate 49.7 L/h (Example 3) [C] Sludge circulation pump flow 184 L/h
rate G/L 0.27 [.alpha.] MLVSS/MLSS ratio 0.4 [.beta.] Amount of
ozone required for 50 mgO3/ MLVSS decomposition gMLVSS [O3 dosage]
Amount of injected 9936 mgO3/ ozone required time [R] Treated
sludge ratio 3.5- [F] Number of times of ozone 6 treatment stage
performed per day [T1] Time period for ozone 1 hr treatment stage
[T2] Miscellaneous time 1 hr [T3] Downtime 2 hr
[0149] Also in Period 2, the treated water quality was stable, and
the BOD removal ratio was generally approximately 95% as with the
case of Period 1 (FIG. 21).
[0150] An excess sludge reduction effect by ozone was obtained, and
in Period 2, the amount of sludge discharged per day was
approximately 400 gMLSS/day, that is, the amount of excess sludge
reduced was 450 gMLSS/day.
Period 3
[0151] In Period 3, the flow regulator was taken off from the ozone
reaction tank and an ozone treatment was conducted. That is, a
treatment was conducted with the same configuration as in the
related art. In addition, also in this period, the aeration tank
MLSS was made constant by discharging sludge. Also in the period,
the ozone treatment conditions were those shown in Table 5 as with
the case of Period 2.
[0152] Also in Period 3, the treated water quality was stable, as
with the cases in Periods 1 and 2 (FIG. 21).
[0153] However, the excess sludge reduction effect was not fully
obtained, and in spite of the amount of ozone injected which is the
same as in Period 2, the amount of sludge discharged per day was
700 gMLSS/day, that is, the amount of excess sludge reduced was 150
gMLSS/day.
[0154] This is because the injected ozone was consumed by the
organic substances leaked from the decomposed microorganisms and
the microorganisms was not fully decomposed. This revealed again
the superiority of the water treatment system according to the
present invention in which a flow regulator is provided in an ozone
reaction tank and an ozone treatment is conducted while separating
and concentrating undecomposed microorganisms by allowing the
undecomposed microorganisms to easily settle.
Period 4
[0155] In Period 4, an ozone treatment was conducted with no flow
regulator provided in the ozone reaction tank as with the case of
Period 3. Furthermore, in view of the fact that the sludge
reduction effect was not fully obtained in Period 3, a treatment
was performed while setting the time period for the ozone treatment
stage [T1] to 2.4 hours, the miscellaneous time [T2] to 1 hour, and
the downtime [T3] to 0.6 hours, so as to make the amount of ozone
injected [O.sub.3 dosage] 2.4 times. The other conditions for the
ozone treatment were the same as in Period 3. Also in Period 4,
MLSS in the aeration tank was made constant by discharging
sludge.
[0156] As a result, the excess sludge reduction effect could be
fully obtained, with the amount of sludge discharged per day being
400 gMLSS/day and the amount of excess sludge reduced being 450
gMLSS/day.
[0157] However, deterioration was recognized in the treated water
quality with the BOD removal ratio being around 80% (FIG. 13). This
is because, among the injected ozone, unreacted ozone remained in
the liquid after the ozone treatment, which lowered the
microorganism activity in the aeration tank.
[0158] In the case where the contact efficiency is low between the
undecomposed microorganisms and ozone in the ozone reaction tank,
as with the case of the related art, a large excess amount of ozone
has to be injected until the sludge reduction effect is fully
obtained, and an amount of ozone will then remain in the
liquid.
[0159] Different modification examples and effects can be easily
derived by a person in the art and are not to be limited to the
specific details and the typical embodiments explained and
described above. Accordingly, various modifications can be made
without departing from the comprehensive concept and scope of the
invention defined by the accompanying claims and equivalents
thereof.
REFERENCE SIGNS LIST
[0160] 1: aeration tank, 2: wastewater, 3: wastewater introducing
path, 4: flow-out path, 5: sedimentation tank, 6: treated water
releasing path, 7: microorganism-mixed liquid, 8: air introducing
path, 9: air diffuser, 10: sludge withdrawing pipe, 11: sludge
withdrawing pump, 12: sludge returning pipe, 13: sludge discharging
pipe, 14: ozone reaction tank, 15: sludge transferring pipe, 16:
sludge extracting pipe, 17: ozone releasing path, 18: sludge
transferring pump, 19: sludge circulating pump, 20: sludge
circulating pipe, 21: treated liquid returning pipe, 22: sludge
introducing pipe, 23: ejector, 24: ozone production device, 25:
ozone transferring path, 26: ozone injecting path, 27: ozone
generator, 28: ozone concentrator, 29: sludge concentration and
separation device, 30: baffle plate, 31: guide pipe, 32: flow
regulator, 33: separated sludge, 34: microorganism-mixed liquid
flow, 35: flow regulating plate, 36: flow regulating cylinder, 37:
microorganism carrier, 38: solid-liquid separation membrane, 39:
filtrate suction pipe, 40: filtering pump, 41: filtrate
transferring pipe, 42: membrane separation tank, 43: membrane
water-feeding path, 44: membrane water-feeding pump, 45:
concentrated sludge returning path, 46 to 52: valve, 53: ozone
injecting branched path, 54: ozone water production unit, 55:
treated water returning path, 56: ozone water transferring path,
57: ozone water feeding pump, 58: ozone gas diffuser, 59: ozone
water tank, 60: treated water, 61: ozone water circulating pump,
62: ozone water producing ejector, 63: ozone water circulating
pipe, 64 to 65: valve, 66 to 69: flowmeter, 70 to 71: valve
* * * * *